Lecture 25: Water Erosion

  • Splash, sheet, rill, gully

Accelerated Soil Erosion and Land Degradation are Global Problems

  • Large amount of croplands worldwide suffer from accelerated or unsustainable erosion
  • Humans are the primary cause of erosion
  • Cost of agricultural land degradation in Canada is 670$ million per year
  • Our food quality is decreasing, less nutrients in soil, less in food
  • Soil loss in the next 40 years in Africa can reduce crops by half

Soil Degradation Has Many Causes

  • Soil degradation results from deforestation, agriculture, overgrazing, chemical contamination
  • Over the past 50 years, soil degradation has become a major problem
  • Grazing practices can contribute to soil degradation

Irrigation Boosts Productivity but can Cause Long-term Problems and Soil Degradation

  • Groundwater depletion
  • Water-logging
  • Salinization - Build up of salts in surface soil layers
  • Salinization inhibits production on 20% of all irrigated cropland, costing more than 11$ billion/yr

Problems with irrigation

  • Expensive
  • Alters root morphology
  • Increase fungal pathogens
  • Can cause salinity problems
  • Subsidence

Remediating Soil Toxicity

  • Salinity
  • Soil PH
  • Heavy metals


  • Type of bioremediation (using living organisms to clean up contaminants)
  • Phytoextraction
  • Drawing chemicals up into plant biomass by action of plants that are hyperaccumulators
  • Hydrangea is a hyperaccumulator of Aluminum


  • Loss of more than 10% productivity of arable land
  • Can be natural or anthropogenic (accelerated desertification)
  • Results from erosion, soil compaction, forest removal, etc...
  • Semi-arid lands are most susceptible (where we live)
  • Over-cultivation causes nutrient depletion

Dust Bowl was a Monumental Event in North American History

  • Rapid mechanization
  • Rapid conversion of grassland
  • Poor agricultural practices

Soil Conservation Council Emerged from Experience of Drought

  • National plan
  • Communication

Crop Rotation

  • Alternating the crops grown in a field from one season or year to the next
  • Cover crops protect soil

Contour Farming

  • Plowing furrows sideways across a hillside perpendicular to its shave to prevent runoffs


  • Cut into hills to form steps to hold water


  • Planting different types of crops in alternating bands

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